That’s a new finding by biologists at the University of Utah, where I work.
Cone snails are abundant in most tropical marine waters, especially around coral reefs. Each species makes a distinct repertoire of venom compounds, mixtures that have evolved to target particular prey. Conus geographus, a cone snail that has killed dozens of people in accidental encounters, traps fish by releasing a blend of immobilizing venoms into the water, according to the prevailing hypothesis. The snail protrudes a stretchy mouth-like part and aims it like a gun barrel at fish, which become disoriented and stop moving even as the snail’s mouth part slowly advances and engulfs the fish.
Seeking to understand how the cone snail springs its slow-motion trap, the Utah researchers searched the gene sequences of all of the proteins expressed in the venom gland of Conus geographus. They found two sequences that looked surprisingly similar to that of the hormone insulin, used by humans and other vertebrate animals to regulate energy metabolism. The insulin genes were more highly expressed in the venom gland than genes for some of the established venom toxins. One sequence proved very similar to that of fish insulin. Chemical analysis of venom confirmed that it contained abundant amounts of this insulin.
Of all the media coverage, The Mary Sue had the most fun with this:
Look at this little guy! Look how sweet he is! So sweet he can kill you with his sweetness. He’s like the deadly version of Hello Kitty, and he would make an amazing villain in an animated Finding Nemo sequel. Let’s make it happen.
Seriously, though, these snails use insulin, among other neurotoxins, in order to debilitate and ingest their prey (including fish! Whole fish!). According to the Proceedings of the National Academy of Sciences, the cone snail produces not only their own snail insulin, but also fish insulin; when a fishy foe approaches, the snail floods the surrounding waters with this insulin, sending the fish into hypoglycemic shock. With crazy low blood sugar, the fish get less glucose to their brain, become lethargic, and the not-so-speedy snails swoop in (well, you know) and swallow their prey…
Baldomero Olivera, a biology professor at the University of Utah who has spent years studying cone snail neurotoxins, came up with great nomenclature for their venoms: ‘lightning-strike cabal’ for the mixture they inject via a harpoon-like organ to rapidly paralyze; ‘nirvana cabal’ for the mixture that some species release into the water to sedate fish. Both C. geographus and C. tulipa (the one starring in the video above) produce an insulin in their venom glands that is very close in structure to that used by fish to regulate blood sugar and energy metabolism.
Every species has a distinct repertoire of more than 100 venom peptides, and cone snails actively adjust the venom mix. Their hunting venom is prey-specific and mostly inactive against humans, for example, but their defensive sting is full of toxins lethal to people. The most deadly snail, C. geographus, can inject a venom dose about 200 times more than necessary to kill an adult human. The venom probably first evolved for defense but then facilitated the evolution of the fish-eating life history.